Reciprocating floor conveyors are now relatively well known and are used in a variety of applications. For example, reciprocating floor conveyors are used in truck-and-trailer vehicles as the floors of the cargo compartments of such vehicles, wherein they are used to load and unload cargo from the compartments. Examples of cargo carried by reciprocating floor conveyors include raw materials, such as pulp and paper products, boxed goods and products loaded on pallets. Reciprocating floor conveyors are also used in garbage-hauling vehicles, as well as in railway cars, to haul solid waste material to a waste disposal site.
Many types of reciprocating floor conveyors have been developed for use in these applications, and these reciprocating floor conveyors employ various methods for controlling the movement of their slat members. An early design for a reciprocating floor conveyor is disclosed in U.S. Pat. No. 2,629,504 of Peterson, granted Feb. 24, 1953. In this patent, a two-slat system is disclosed wherein the reciprocating floor conveyor includes two sets of slats. Both sets of slats are moved forwardly to convey the load, and then one set of slats is moved backwardly, while the other set is held stationary. Then the other set of slats is moved backwardly, and the cycle is repeated to move the load further along the conveyor.
West German Patent Publication 1,296,087 ('087), issued May 22, 1969, discloses a four-slat system. In this system, three sets of slats are always moving forwardly at any given time, while one set of the slats moves backwardly. The sequence of the backwardly-moving slats is rotated among the four slat members, so that three of the slat members are always moving forwardly to convey the load. U.S. Pat. No. 3,534,875 of Hallstrom, Jr., granted Oct. 20, 1970, discloses a three-slat system that uses the same principle as that of the West German '087 patent.
U.S. Pat. No. 3,905,290 ('290) of Caughey, granted Sep. 16, 1975, and U.S. Pat. No. 4,709,805 of Foster, granted Dec. 1, 1987, both disclose a four-slat system wherein all of the slats move forwardly together to convey the load, and then each of the four sets of slats sequentially moves backwardly until all four sets are in a back position, and then the cycle is repeated. U.S. Pat. No. 4,143,760 of Hallstrom, Jr., granted Mar. 13, 1979, discloses a system similar to that disclosed in the Caughey '290 patent, but with three sets of slats, wherein all three sets of slats move forwardly and each set sequentially moves rearwardly.
U.S. Pat. No. 4,962,848 of Foster, granted Oct. 16, 1990, discloses a reciprocating floor conveyor having three sets of slats, with one set of slats permanently fixed in position, and the other two sets of slats are movable forwardly together and backwardly independently. All of the above-discussed patents, which are incorporated herein by reference, utilize the same basic principle of having a greater number of slats stationary or moving forwardly than are moving backwardly, when some slats are moved backwardly in a nonconveying mode.
While the foregoing reciprocating floor conveyors work satisfactorily in conveying a wide variety of loads, certain types of loads can be damaged at the transition ends of these conveyors where the loads move off of or onto the conveyors. At the transition ends of the conveyor, the ends of the slats can either be even or staggered, depending on the stage of the conveyor in its operating cycle. By way of example, FIGS. 1-4 in U.S. Pat. No. 4,962,848 illustrate how the ends of the slats are staggered at certain points in their operating cycle. It has been found that for certain materials, the staggered configuration at the transition end of the conveyor can damage the load being conveyed. For example, as the slat members move back and forth, the forward corners of the slat members and the sharp side edges of the slat members can cut, tear, scratch, or puncture the load being conveyed. This problem has been particularly troublesome for large rolls of paper, which are relatively delicate compared to crates, for example, and thus, can be easily damaged by a sharp object.
In addition, certain loads are somewhat flexible in nature and, thus, tend to sag in the gaps between the offset, forward ends of a set of slats. This, in conjunction with the sawing-like action of the slat members, increases the potential of the slats damaging the load.
Accordingly, a principle object of the present invention is to provide a reciprocating floor conveyor that avoids these problems when conveying certain types of material.